The automotive industry, for a number of years, has desired glass having grey color (sometimes called “neutral grey”) for automotive window applications. In certain situations, it is also desirable to have grey colored glass for architectural window applications. At the same time, it is also desirable for transmission in the UV and/or IR ranges of the light spectrum to be minimized.
A glass window or other glass article is said to have the desirable color “grey” when it has a dominant wavelength of from 435 nm to 570 nm (this dominant wavelength range defines the color “grey” herein). Moreover, grey glass often has an excitation purity of less than about 4.5%. In certain embodiments, it may be preferable to have a dominant wavelength of from 470 nm to 570 nm, or even from 480-560 nm, with purity of from about 0.2 to 4.5%.
While glass having “grey” color is often desirable, there sometimes also exists a need or desire to achieve solar control for architectural and/or other applications. Example solar control parameters include:
Lta as visible light transmission,
SHGC (Solar Heat Gain Coefficient) (Air Mass 1.5), and/or
IR as infrared light transmission.
Glass thickness ranges of from about 1-6 mm, more preferably from about 3-4 mm, are typically used when measuring the aforesaid characteristics. These thickness ranges are generally recognized as conventional thicknesses for glass sheets made by the float glass process, as well as recognized thickness ranges in the automotive and/or architectural industries.
For certain example non-limiting architectural applications, it is often desirable for a glass to realize one or more of the following characteristics at one or more of the aforesaid thicknesses:
Lta: at least about 55% (more preferably >=about 60%, or 65%)
SHGC no greater than about 0.67 (more preferably <=0.65, or 0.64).
Classically formulated grey glasses often include low levels of iron (i.e., less than 0.2% total iron) along with cobalt and nickel oxides. Unfortunately, while this type of glass may achieve satisfactory coloration in certain instances, it typically suffers from undesirable solar characteristics (e.g., too high of a SHGC—typical grey glass has an SHGC around 0.8 at 4 mm thickness). Certain nickel-free grey glasses combine selenium (Se) and cobalt (Co) oxide with iron oxide, but also suffer from poor solar performance characteristics.
In view of the above, it is apparent that there exists a need in the art for a glass composition which may achieve desired grey color in combination with an improved SHGC and/or visible transmission.